Box bottom composite sack

ABSTRACT

A box bottomed composite sack manufactured with a combination of monoaxially oriented tape fabric and non-oriented materials, and having a cover sheet bonded to the box bottom, is disclosed. The box bottomed sack is preferably constructed with either monoaxially oriented tape fabric or non-oriented material and can be coated on either side with a thermoplastic material such as polypropylene, polyethylene, ethylene vinyl acetate, and polyolefin to seal the sack and to facilitate bonding to the cover sheet. The cover sheet can be constructed with any suitable material, selected so that either the cover sheet or the sack body is made of monoaxially oriented tape fabric, and attached to the folded box bottom of the sack by a corresponding method for the specific cover sheet material. The cover sheet can be coated with thermoplastic material to facilitate bonding to the sack. The composite box bottomed sack does not require costly equipment to manufacture, is less susceptible to weakening due to heat treatment and is economical.

FIELD OF THE INVENTION

The present invention relates generally to composite sacks for packaging of bulk material. More particularly, the present invention relates to composite sacks having a box shaped end.

BACKGROUND OF THE INVENTION

Sacks are commonly used to pack bulk material for storage or transportation, and have capacities anywhere between 10 to 1000 kilograms for example. These sacks can take on different shapes, such as pillow and box shapes. A pillow shape is typically created by manufacturing the bottoms with seams. A box shape is created by folding and bonding the bottom into a block form. Those of skill in the art will understand that a box shape optimizes use of the material surface, facilitates stacking and provides improved utilization of volume due to its brick shape. A variant of the box shape sack is the quasi-box shape which is a pillow sack on one side and a box sack on the other.

There is a wide variety of literature regarding box bottomed bags, including the following patents.

U.S. Pat. No. 3,195,801 to Symons et al. discloses a bag formed from heat sealable thermoplastic material. The material is folded to form four side walls and an open rectangle at each end of the tube. At least two of the four edges of each rectangular bottom are heat-sealed along their length to two of the sidewalls. A separate rectangular cover sheet, made of the same thermoplastic material, is then aligned and superimposed upon the open rectangle to provide a sealed bottom. The bag may also provide a single valve located in one of the corners of the bag. The valve is used to facilitate the filling of the bag with granular or pulverulent materials. The bag disclosed in Symons is atypical of box bottomed bags in that most box bottomed bags and sacks are formed from a tube whose open ends are folded to close the end. The closed end is then sealed with a cover sheet. While Symons teaches a means for creating a sack with less material, the simple heat seal typically does not provide structural rigidity. When a filled bag is rotated so that the sealed end is substantially bearing the load, the heat sealed section of the two fabric pieces must bear all the load, which puts great stress on the seal itself. As a result, the choice to not fold over the ends of a tubular section of fabric results in both a loss of rigidity and a loss of end strength.

U.S. Pat. No. 3,397,622 to Goodwin discloses a bag made of flexible heat-sealable sheet plastic material such as polyethylene. At the top and bottom closures of this bag, a rectangular cover made of the same heat sealable sheet plastic material (e.g. polyethylene) is applied. Strips of heat seal inhibiting material are attached at two edges of these ends of these covers so that they may attach to the bag closures. The top closure of the bag also contains a valve flap which is used for filling purposes. The bag is completed by folding over the top and bottom side flaps and creating heat seals where the flaps overlap. Polyethylene is not typically used in oriented fabrics and thus does not typically provide the strength required for heavy loads.

U.S. Pat. No. 3,448,666 to Kappelhoff discloses a cross bottom sack with a tube length made of thermoplastic material, preferably of polyolefins. The open ends of the tube are pre-treated with coatings of an adhesive, which is effective in a dry, or almost dry condition. After the treatment, the tube end portions are folded along the intended fold lines to form open crossed tops and bottoms with infolded corner portions. To close the top and bottom portions, the side flaps are folded over towards the middle and are adhered to by the adhesive coated surfaces. The bottom portion is completed by attaching a bottom covering sheet, which has been pre-treated and provided with the adhesive layer. The use of adhesives limits this bag and its applications. As previously mentioned, in many fields the materials stored in the bags are provided at a temperature that causes the adhesive to liquefy, and the adhered bond to be dissolved. As a result, the application of an adhesive makes the bag unusable in applications where the contents for storage are provided at high temperatures.

U.S. Pat. No. 3,660,150 to Cooper discloses both a coated woven material and a method for producing the coated woven material. Cooper teaches the a laminated web consisting of a woven layer and a continuous thermoplastic coating, and discloses the use of this material in bags and sacks, such as the bags and sacks taught in the other references. Cooper is directed to the actual coated woven fabric, and not to the construction of the sacks per se.

U.S. Pat. No. 3,736,219 to McTaggart discloses an apparatus that provides a strong, flexible, heat resistant seal for uncoated oriented polyethylene terephthalate film. The seal is created by first superposing polyethylene terephthalate films and cutting off a portion of the two films to provide uniform congruent edges. The films are then passed over a heat sink whereby the edges of the two films become fused thus forming a heat seal. Finally, the heat sealed film is then passed over a cooling station. At this stage, the heat sealed film can either be wound up on a roll or alternatively folded, trimmed and sealed to form a tube. Though McTaggart does teach the sealing of an oriented polyethylene film, the resulting sealed film cannot be used in the production of sacks and bags that are used to contain heavy loads, as the oriented film is insufficiently strong.

U.S. Pat. No. 4,270,677 to Schmidt discloses a reclosable cross-bottom sack. The sack consists of a square base with two side flaps. When the side flaps are folded onto the base, their end faces are spaced from each other forming a channel. Within this channel is an internal lock where a base cover sheet along with a base closure lock can be applied. This results in the base closure lock bridging the space left vacant by the base side flaps. The base cover sheet is attached by means of a two component adhesive. To open the sack, the closure lock is pushed into a position in which its hole is disposed substantially near the middle of the base. At this point, a corresponding hole in both the cover sheet and the internal lock is made to let out the contents of the bag. In order to close the hole, the closure lock is pulled away so that its hole leaves the vicinity of the pierced holes. As earlier described, the use of an adhesive limits the applications for which the sack can be used.

U.S. Pat. No. 4,235,366 to Achelpohl et al. discloses a plastic sack made from a coated tube of woven tape. The tube when opened, forms a square base outlined by two triangular corner tucks. An internal closure member is welded to the edges of the corner tucks by weld seams. The base is closed by folding two side flaps one at a time. The first side flap is folded onto the tube's base. Afterwards, a base cover sheet with releasable adhesive in its interior is then applied over the base. Finally, the second side flap is folded on top of the base cover sheet and secured by dabs or strips of glue. A weld seam is also applied to close the end of this base side flap. The sack taught by Achelpohl et at. is clearly directed to the use of laminated drawn plastic tapes to form both the sack and the coversheet.

U.S. Pat. No. 4,284,229 to Schmidt et al. discloses a reclosable cross bottom sack with a tube section of plastic material or plastic tape fabric. The closed cross bottom is formed by folding and adhering the side flaps of the tube section. The base cover sheet is also made of plastic material or plastic tape fabric and is laminated or adhered to a film of plastic material on the base. A central slit in the cover sheet is provided to connect the sack to a separate side tube. This is accomplished by pushing the ends of the side tube through the slit until these ends lie flat on the inside of the base. The side tube is also connected to the base cover sheet by means of weld seams. The purpose of this side tube is to provide a means of partially or completely emptying the contents of the sack. Additionally, Schmidt et al. discloses the use of an inner sack of plastic film used to allow opening and closing of the sack for partial filling or emptying. However, Schmidt et al. is also clearly directed to the use of laminated drawn plastic tapes to form both the sack and the coversheet.

U.S. Pat. No. 3,979,049 to Achelpohl discloses a closed cross bottom bag. The bottom end consists of two side fold portions, a square base portion and two triangular corner tucks. To completely close the bottom end, a strip of hot melt material is first applied to the corner tucks. This is followed by folding the two side fold portions over onto the square base portion. Finally, a cover sheet with strips of hot melt material at the edges is adhesively secure to the tucked and folded portions of the bottom. This is achieved by aligning the strips of hot melt material on the cover sheet with those on the corner tucks so that the exposed part of the coatings come into contact. As described above, the use of an adhesive, such as that described in Achelpohl et al., typically provides a seal that is insufficiently strong for use in hot fill environments. Additionally, Achelpohl et al. teaches the use of tape based fabrics for both the coversheet and the sack body.

As shown above, it is known in the art to coat materials, such as monoaxially oriented drawn tape woven fabrics as well as natural fabrics, to produce a material that is both strong and impermeable. One technique for laminating such a material is disclosed in Canadian Patent No. 1,133,369 to Stead et al. Stead et al. teaches the lamination of knitted, woven or folded fibres of cotton, wool, glass, polypropylene, nylon, polyethylene terephthalate, polyacrylate or mixtures of two or more such fibres. Melded cloth such as Cambrelle is also suitable for the process described by Stead et al. In one of the procedures, a web of unfilled polypropylene is sandwiched between a sheet of filled polypropylene composition and a cloth. While being sandwiched, the heat from the filled polypropylene causes the boundary between the sheet and the web to become insignificant. As a result, on cooling, the laminate is formed.

As described above, sacks are commonly manufactured with plastic fabrics consisting of monoaxially drawn tapes. The tapes are typically polypropylene tapes. Drawn tapes have high strength in one dimension due to the aligned orientation of its molecular chains resulting from the drawing process. A fabric is woven from weft and warp tape “threads”. This fabric has high load bearing strength and two dimensional stability resulting from the perpendicular warp and weft tapes. To prevent seepage of the contents of the bag, the fabric is sealed, typically using a polyethylene laminate. The folded bottom of box shaped sacks preferably use a cover sheet of the same material as the sack that is thermally bonded to it for providing mechanical strength and durability.

Cover sheets are used so that additional strength is provided at the ends of the bag so that the box bottom folding does not become undone in shipping. The coversheets must be bonded in such as way that they both provide strength and at the same time must be economical. Though one option for adhering the coversheet is the use of adhesive compounds such as glue, it has been found that the warm packing of cement, a common content for box bottomed tape fabric sacks, introduces the cement at a temperature that melts the glue, and results in the weakening of the coversheet bond. As a result, gluing of a coversheet is not considered feasible, and the thermal attachment of a tape fabric cover sheet is employed. Adhesives that do not melt in this temperature range are typically considered to be too expensive to be cost effective.

U.S. Pat. No. 5,845,995 to Starlinger Huemer discloses a box bottomed bag made of a monoaxially oriented drawn tape woven fabric that has coversheets, of an identical material, heat fused to the sack body. Although Starlinger Huemer teaches the controlled heating and pressing of the sack body and coversheet to minimise the amount of disorienting that occurs as a result of the application of heat in the sealing process, an analogous technique is used for other applications of woven tape fabrics, such as in the manufacture of synthetic tarpaulins.

In the adhering process, a coversheet made of coated tape fabric similar or identical to the fabric of the sack is attached to the bag using a heat and pressure process to fuse the coversheet to the sack. In the heating process, the polyethylene coating of the bag and coversheet melt and bond. Additionally, the small amount of polyethylene in the fabric is drawn to the surface allowing the sack and the coversheet to be securely bonded. If done carefully, the, heat and pressures used in the process will be above the threshold at which polyethylene melts, but below the threshold at which polypropylene melts. This prevents holes from developing in the sack or the coversheet.

Unfortunately, the plastic fabric tapes are susceptible to heat in a manner unrelated to causing holes. A heating process is used during the drawing of the fabric tape to obtain the monoaxial orientation of the polymer chains that provides strength. During the heating process to adhere the coversheet the monoaxial orientation of the molecular chains in the tapes can be lost, resulting in loss of fabric strength. The thermal bonding process thus requires precise control over parameters such as heating temperature, heating time and pressure for the specific thickness of the fabric tape to minimize molecular disorientation. Unless specific equipment is used, unreliable bonds can be formed and defective sacks will be manufactured therefrom. Starlinger teaches the use of costly equipment for the reliable adhering of coversheets. Additionally, the monitoring and control systems required are relatively expensive and technically complex. Further adding to the cost of manufacturing plastic fabric tape sacks is the equipment required for manufacturing the plastic tapes.

Alternate methods of attaching the coversheet have typically been viewed as undesirable. As discussed above, gluing the coversheet is unsuitable in cases where the sacks are to be warm filled, as the adhesives used in this process tend to dissolve at the produced temperatures. Though advanced adhesives can be used, they are typically more expensive, and are thus considered relatively undesirable. Stitching a laminated coversheet to a laminated fabric sack will adhere the coversheet with sufficient strength, but the stitching perforates the sack and thus reduces the impermeability of the sack achieved through lamination. Though the stitches can be covered by an adhesive tape, this introduces another expense which is undesirable.

While plastic tapes are a suitable material for sacks, they are not abundantly available in certain parts of the world, especially in third world countries where industrial development drives the need for large amounts of inexpensive high volume packaging. Although paper is an alternative material to plastic, trees required to make paper can be scarce and their use in the manufacture of paper is environmentally detrimental. The highly automated processing required to produce reliable box bottom sacks made from monoaxially oriented tape fabrics, is considered cost effective in some parts of the world, but in many parts of the world, the material costs are considered to be high, as are both the cost of the machinery, and the cost of a reliable power supply required to keep the process operating efficiently.

In the interests of reducing costs, taking advantage of local variations in the costs of materials and labour, sacks are ideally manufacturable with a readily abundant material, and with low cost equipment and methods. The use of a fabric that is not as susceptible to loss of strength due to heat sealing as polypropylene tape fabrics are would also be beneficial. Thus, it would be desirable to provide a box bottomed sack or bag that can be created without strict reliance on the use of laminated woven tape fabric, requiring difficult to implement coversheet attachment.

It is, therefore, desirable to provide a box bottomed sack or bag that can be created at a lower cost and in greater harmony with concepts of appropriate technology and environment friendliness by taking advantage of regional differences in the above factors.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at least one disadvantage of previous box bottomed sacks. In particular, it is an object of the present invention to provide a box bottomed sack that minimises the reliance on materials that are scarce, difficult to produce, difficult to work with and environmentally unfriendly.

In a first aspect of the present invention, there is provided a box bottomed sack. The sack comprises a sack body and a cover sheet. The body has one end folded into a box bottom configuration, preferably including a self closing valve, and is constructed from a material selected from a list including a monoaxially oriented woven tape fabric, fabrics made from cotton, jute, hemp, nylon and polyester. The cover sheet is attached to the folded end of the sack body, and is constructed from a material selected from a list including a monoaxially oriented woven tape fabric and fabrics made from cotton, jute, hemp, nylon, polyester and non woven, paper, film and foil. The material selected so that exactly one of the sack body and cover sheet are constructed from a monoaxially oriented woven tape fabric.

In an embodiment, the sack further includes a liner, that is optionally micro perforated, and is attached to the sack body by preferably stitching and is larger than the sack body in at least 1 dimension. In this embodiment, the folded end of the sack body includes a self closing valve that opens to the interior of the liner. In another embodiment, the liner is affixed to the sack prior to folding the edges.

In another embodiment, the cover sheet is attached to the sack body by an attachment method selected from a list including gluing, sewing, tacking, taping and slit die extrusion.

In a further embodiment, either one or both the sack body and the cover sheet are laminated by a thermoplastic material selected from a list including polyethylene, polypropylene, polyolefins, and ethylene vinyl acetate. In this further embodiment, the cover sheet is preferably attached to the sack body by fusing the lamination of the sack body and the cover sheet by an method selected from a list including heat sealing, ultrasonic plastic welding, heating plate pressing, heat plate pinning and friction welding.

In another embodiment, the sack body has both its ends folded into a box bottom configuration, and the sack further includes a second cover sheet that is attached to the second folded end of the sack body, the second cover sheet selected from a list including a monoaxially oriented woven tape fabric and fabrics of cotton, jute, hemp, nylon and non woven, paper, film and foil.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:

FIG. 1 is an orthogonal view of a box bottom sack according to an embodiment of the present invention;

FIG. 2 is an orthogonal view of the box bottom sack of FIG. 1 showing a valve location in the box bottom sack of FIG. 1;

FIG. 3 is an orthogonal view of a length of fabric and liner used to manufacture the box bottom sack of FIGS. 1 and 2;

FIG. 4 is an orthogonal view of the length of fabric of FIG. 3 with the liner stitched to the fabric;

FIG. 5A is a plan view of the fabric of FIG. 3, with an unsealed liner, in a partially folded state;

FIG. 5B is a plan view of the fabric of FIG. 3, with a sealed liner, in a partially folded state;

FIG. 5C is a plan view of the fabric of FIG. 3, without a liner, in a partially folded state;

FIG. 6A is a plan view of the partially folded fabric of FIG. 5A with a valve;

FIG. 6B is a plan view of the partially folded fabric of FIG. 5B with a valve;

FIG. 6C is a plan view of the partially folded fabric of FIG. 5C with a valve;

FIG. 7A is a plan view of the fabric of FIG. 6C in a subsequent folded state FIG. 7B is a plan view of the fabric of either of FIG. 6A or 6B in a subsequent folded state;

FIG. 8 is an end view of the fabric of FIG. 7 in a completed folded box bottom configuration; and,

FIGS. 9-12 illustrate methods of bonding a cover sheet to the sack.

DETAILED DESCRIPTION

The present invention provides for a box bottomed sack or bag that can be manufactured without complete reliance on coated woven tape fabric. As discussed above, this fabric is typically selected for its strength and its ability to prevent the seepage of its contents. There are a range of other woven fabrics made of non-oriented fibres that can be used, and are more readily accessible in many parts of the world. These fabrics include cotton, hemp, jute, other commonly used natural fibres as well as synthetic fibres such as nylon and polyester. These fabrics can be manufactured locally in many parts of the world where labour costs are lower, and then used to form the body of the bag. To prevent seepage, these fabrics can be coated on either a single side, or both sides, with a thermoplastic material such as polyethylene, polypropylene, E.V.A. to seal the sack and to facilitate bonding to the cover sheet. The cover sheet can also be constructed with any suitable material, such as those listed above, and attached to the folded box bottom of the sack by a corresponding method for the specific cover sheet material. The cover sheet can be coated with thermoplastic material to facilitate bonding to the sack. The box bottomed sack constructed using natural fibres does not require costly equipment to manufacture, and is less susceptible to weakening due to heat treatment and is friendlier to environment.

It is however generally acknowledged that the use of woven oriented tape fabric has advantages. In contrast to many natural fibres, oriented tape fabric has a low weight to strength ratio, which is desirable. It has been found, that a mixing of materials provides some of the benefits of both fabrics. By building the sack body from woven tapes, and a coversheet from a natural fibre fabric, the overall sack weight is kept low, but the ends of the bag have increased flexibility, which helps with the handling of the bags. Additionally, as the cost of the materials fluctuate, costs can be lowered by changing from a woven tape sack body and natural fibre fabric coversheet, to a woven tape coversheet and a natural fibre fabric sack. One skilled in the art will appreciate that synthetic fabrics such as polyester and nylon can be used in place of the natural fibre fabric to bond to the oriented tape fabric while providing many of the same benefits.

Thus, the creation of a box bottomed sack where one of the sack and coversheet are made from woven monoaxially oriented tapes, while the other is made of a non-oriented fibre fabric can provide a mixture of benefits, and can allow for cost based variation.

As in prior art implementations, coversheets can be adhered to the sack body using by bonding the elements using heat and pressure. By proper coating of the non-oriented fabric, a simpler process, with a larger margin of error is possible. This allows the process to be performed either by a machine or manually, so that in markets with low labour costs the sacks can be assembled by handheld tools.

In another embodiment of the present invention, seepage is prevented without the lamination of the sack body and coversheet. If both the sack body is left unlaminated, it will not be able to prevent the seepage of its contents during shipping, handling and under other forms of pressure and stress. The limiting factor for this process is the size of the pores created in the weave of the fabric. For large size granules, such as rice grains, tapioca beads and other food stuffs, it is possible to simply provide a tight weave in an unsealed fabric so that the contents cannot seep. For smaller grain contents, such as powders, a seal cannot be introduced by simply creating a tighter weave. While previous attempts at preventing the seepage of powders such as cement have focussed on sealing the fabric used to create the sack through lamination, one embodiment of the present invention addresses the issue by introducing a sack liner. Those skilled in the art will appreciate that liners can easily be created with small pores, commonly referred to as micro-pores, at a low cost, so long as the liner is not overly strong. This has traditionally been viewed as a detriment as a weak liner will tear under the pressure of a large load. However, if the liner is larger than the an unsealed sack, in at least one dimension, the liner can be used to prevent seepage, and the unsealed sack can be used to provide the load bearing strength without needing to prevent seepage. One skilled in the art will appreciate that the thickness of the liner can be varied, but is typically on the order of 5 to 100 m.

It will be apparent to those familiar with present box bottomed sacks that they are typically designed to be self closing, and are filled through a valve in their top fold. The valve typically has a flap that, under the pressure of the contents, closes to prevent the contents from leaking. To attach a liner, prior to the folding of the box edge and the attachment of the self sealing flap, a liner can be sewn into the fabric so that it is held in place during loading. If the top of the sack is to be a box form, the liner is attached prior to the folding of the end of the sack. As the loading of fine particulate matter is typically done through a mix of gravity and blowing, in a presently preferred embodiment, the liner has vents to allow for the escape of the forced air. Though it is acknowledged that the contents of a loaded sack may escape through these vents, it is also recognised that the contents then have to work their way through the load bearing sack. This double barrier provides sufficient protection from seepage to meet requirements of most applications.

The present invention provides two methods of attaching a liner to the interior of the sack. In the first embodiment, the liner used is larger than the sack in at least one dimension, so that the load of the contents is borne by the sack, and the liner need not be overly strong. In this embodiment, the liner has both an open and a closed end, and the closed end is inserted into the sack body, either before or after the end of the body has been closed. The open end of the liner is then affixed to the sack body, and the end of the sack body is folded into form. Preferably, the end at which the liner is affixed is provided with a self closing valve. In an alternate embodiment, neither end of the liner is closed. Instead, the liner is inserted into the sack body before either end is sealed. The liner is affixed to the sack body, and the ends of the sack body are then folded closed. In this manner, the sack is provided with a liner along its full length.

An alternate method of attaching the coversheet to the sack is now described. If the sack body is unlaminated, and a laminated coversheet is used, a heat sealing process can be implemented as before, and if sufficient lamination is present on the coversheet, it will impregnate the sack body and seal the two together. The same is true if the sack body is laminated but the coversheet is not. In instances where neither the coversheet nor the sack body are laminated, they can be stitched, glued, tacked or bonded through slit die extrusion.

Thus, the present invention provides for a box bottomed sack that seals the contents either through a tight weave, through a liner bag, or through coating of the fabric of the sack. The sack itself can be created from fabrics available in a local environment and does not require expensive manufactured monoaxially oriented tapes. In the following description, the design of the above described sacks is presented, and one skilled in the art will appreciate that the manufacture of these sacks can be automated, but can also be performed through the use of local labour when labour costs make this an attractive option. The sealing of woven tape fabrics to other woven tape fabrics is known in a number of arts, including that of synthetic tarpaulin manufacture, and is applicable to the present invention.

As should be known to those of skill in the art, a box bottom sack is generally constructed with a seamless tubular fabric or flat fabric combined to form a tube, where at least one end of the sack has its ends folded to form a rectangular bottom surface.

FIGS. 1 and 2 are drawings of a box bottomed sack according to embodiments of the present invention. In FIG. 1, sack 100 includes a sack body 102, a box bottom end 104 and a top end 106. Box bottom end 104 can be folded by any known method known to those of skill in the art, and a cover sheet 108 is attached to box bottom end 104 to secure the folds. While the top end 106 is shown in a box, or block configuration, top end 106 can be configured in a pillow shape, or any desired configuration. According to an embodiment of the present invention, sack body 102 is constructed from a fabric such as cotton, hemp, jute, or from a woven tape fabric, while cover sheet 108 is constructed from a fabric selected from the same list, which may optionally be augmented by the inclusion of paper, films and foils, but selected so that cover sheet 108 and sack body 102 are not both made from a coated monoaxially oriented woven tape fabric. Preferably, one of the sack body 102 and the coversheet 108 are monoaxially oriented woven tape fabrics. Many different methods can be used to attach cover sheet 108 to sack body 102. For example, a natural fibre fabric cover sheet 108 can be stitched, tacked or clipped, or bonded through slit die extrusion or if cover sheet 108 and sack body 102 are both coated to prevent seepage, they can be heat sealed so that the sealing compound that permeates both fabric pieces adheres to form a bond.

According to one embodiment, a low cost natural fibre fabric sack body 102 can be manufactured because it is not coated with a laminate material to seal it. Alternatively, the natural fibre fabric sack 100 can have its external surface laminated, its internal surface laminated, or both the internal and external surfaces laminated. The laminate material can be any suitable thermoplastic material, such as polyolefins like polyethylene and polypropylene as well as other known coatings such as ethylene vinyl acetate (EVA) and copolymers. These coatings, when coated onto sack body 102, prevent fine particulate matter from seeping. While a cover sheet 108 can be attached to the sack body 102 by the previously described attachment methods, the cover sheet 108 can be laminated with the thermoplastic material and attached to the laminated or unlaminated box bottom 104 by appropriate attachment means such as heat sealing, ultrasonic plastic welding, pressed means such as a heating plate or pin, or friction welding for example. Of course, stitching, clipping, and tacking methods can be used to attach the laminated cover sheet 108 to sack body 102. In an alternate embodiment, cover sheet 108 can be constructed with a plastic material laminated with thermoplastic material, and then attached to sack body 102 with the previously mentioned techniques.

FIG. 2 shows the features of box bottom 104 illustrated by dashed lines, that are hidden by cover sheet 108. Box bottom 104 preferably includes a valve 110 disposed over folded side flap 112, and a top flap 114 folded over valve 110. Finally, a bottom flap 116 is folded over top flap 114. Valve 110 permits insertion of a pipe into the interior of sack body 102 while the sack 100 is empty for delivery of material, while effectively preventing seepage or escape of material once the sack 100 is full and the box bottom 104 is placed on a surface. The weight of the material will press valve 110 upon the top and bottom flaps 114 and 116 to close valve 110 when sack 100 is filled.

Another method of sealing sack 100 is to incorporate a liner into the interior surface of sack 100. Liners are well known in the art, and can be any material to suit the material being packaged.

FIG. 3 is a drawing of a sack body 102 and a liner 120 prior to assembly. Preferably, liner 120 is a thin plastic material and shaped to be larger in volume than the sack body 102. The larger liner size ensures that the load of the material is supported by the sack body 102, since the liner 120 is relatively weak in comparison to the material of sack body 102. The liner 120 can be sealed at the edge 122 to prevent the packaged material from escaping.

As described above, the liner 120 can also be inserted into the sack body 102, with no closed end, and affixed to both ends of the sack body 102 prior to folding. The sack body 102, with liner 120 affixed can then be folded and sealed in the desired manner to form a sack 100 with an affixed liner.

FIG. 4 is a drawing of liner 120 attached to the interior surface of sack body 102. After the liner 120 is inserted into the interior of sack body 102, the liner is hemmed with stitches 124 near the periphery of sack body 102, except at the end where the liner 120 protrudes from sack body 102. Although the liner 120 is shown attached to sack body 102 with stitches 124, liner 120 can be sealed, glued, heat sealed or clipped to sack body 102. In a presently preferred embodiment, bulk material can then be used to fill the sack 100 through its filling vent. In an alternate embodiment, liner 120 is attached to sack body 102 as described above. The top of sack body 102 is not closed, so the bulk material can fill the sack 100 through the un-hemmed edge of sack body 102 and liner 120. Once liner 120 is filled, sack 100 can be closed to form a box bottomed end. This configuration removes the requirement for a valve.

FIGS. 5 to 10 illustrate the steps for folding the end of sack body 102 of FIG. 4 into a box bottom configuration.

FIGS. 5A, 5B and 5C show the flat sack body 102 of FIG. 4 in a partially folded state where an open end of sack body 102 has its side flaps 112 folded towards each other to expose the interior surface 130 of sack body 102 and optionally liner 120. As previously shown in FIG. 4, liner 120 is attached to sack body 102 via stitches 124. In particular FIG. 5A shows the embodiment where sack 100 has an unsealed liner 120 that is affixed to the sack body 102. The liner as illustrated in FIG. 5A is unsealed, and the subsequent folding of the sack will provide a folded over liner end, so that the bulk material will be substantially prevent from seeping. In FIG. 5B, the embodiment of a sealed sack liner is illustrated. The liner 120 is inserted into sack body 102 as before, but the bottom end is sealed at edge 122 to prevent seepage of the packaged bulk material. FIG. 5C illustrates the embodiment where no sack liner is used.

FIGS. 6A, 6B and 6C show the partially folded state of sack body 102 of FIG. 5 after attachment of valve 110. Valve 110 is a sheet of material that is placed over one of side flaps 112, after the side flaps 112 have been folded towards each other. Valve 110 can be formed in any shape and in any desired size. FIG. 6 further shows the top and bottom flap fold lines 132 whereby the top and bottom flaps are folded towards each other in a subsequent folding step. FIG. 6A illustrates the partially folded state of sack body 102 with the unsealed liner, as shown in FIG. 5A. FIG. 6B illustrates the partially folded state of sack body 102 with the sealed liner, as shown in FIG. 5B. FIG. 6C illustrates the partially folded state of sack body 102 without a liner, as shown in FIG. 5C.

FIGS. 7A and 7B show sack body 102 after the top flap 114 and the bottom flap 116 are folded towards each other along the top and bottom flap fold lines 132. It is noted that valve 110 is also folded along the same fold lines 132 as top flap 114 and bottom flap 116. Preferably, one of the flaps is folded to overlap the other flap as shown in FIG. 7. It should be obvious to those of skill in the art that the position of fold lines 132 can be selected to determine the amount of overlap between the top flap 114 and bottom flap 116. After top flap 114 and bottom flap 116 are folded, sack body 102 is folded along side edges 134 to complete the box bottom configuration of sack 100. FIG. 7A illustrates sack body 102 without a liner, while FIG. 7B illustrates sack body 102 with liner 120

FIG. 8 shows the box bottom 104 of sack body 102 after cover sheet 108 is attached to cover side flaps 112, top flap 114 and bottom flap 116. As previously mentioned, cover sheet 108 can be glued, stitched, or clipped to box bottom 104 if unlaminated, or can be attached through heat sealing, ultrasonic plastic welding, pressed heating plate or pin, or friction welding to box bottom 104 if cover sheet 108 is laminated.

FIGS. 9 through 12 illustrate methods for attaching cover sheet 108 to box bottom 104 according to embodiments of the present invention. More specifically, the methods use rollers to press the cover sheet 108 to box bottom 104 as heat is applied to the surfaces to be bonded.

In FIG. 9, a cover sheet 108 laminated with thermoplastic material 140 and a box bottom 104 laminated with the same or different thermoplastic material 140, are rolled between a pair of rollers 142 as heat 144 is applied to the lamination material 140. The cover sheet 108 and the box bottom 104 are drawn in the direction of arrow 146 at a predetermined rate. The heat sufficiently melts the thermoplastc material 140 and the rollers 142 press the cover sheet 108 and the box bottom 104 together to form an intimate bond. The rollers can be cooled to accelerate the bonding process.

In FIG. 10, a cover sheet 108 laminated with thermoplastic material 140 and an unlaminated box bottom 104, are rolled between a pair of rollers 142 as heat 144 is applied to the lamination material 140 of cover sheet 108. The melted thermoplastic material 140 will bond to the box bottom 104 as it is drawn and pressed between rollers 142. Alternatively, the box bottom 104 can be laminated while the cover sheet 108 is unlaminated.

In FIG. 11, an unlaminated plastic cover sheet 108 and an unlaminated plastic fibre fabric box bottom 104, are rolled between a pair of rollers 142 as heat 144 is applied to the material. The heat is sufficient to melt some of the plastic material of the cover sheet 108 and the box bottom 104 such that they will bond together as they are drawn and pressed between rollers 142.

In FIG. 12, an unlaminated plastic coversheet 108 and an unlaminated box bottom 104, are rolled between a pair of rollers 142. The lamination material 140 is extruded through a slit die between coversheet 108 and box bottom 104. The pressure exerted by rollers 142 and the heat that is applied is sufficient to melt lamination material 140 so that it permeates both coversheet 108 and box bottom 104 and secures them to each other.

It is noted that the material of the cover sheet 108 and the sack body box bottom 104 shown in FIGS. 9 through 12 can be a natural fibre fabric or plastic material, where any combination of cover sheet material and sack body material is possible.

Since natural fibres are readily available in many developing countries, box bottomed sacks constructed of natural fibres fabric will have a low material cost in some countries when compared to sacks constructed with less abundant materials, such as plastics. Natural fibre fabric sacks can withstand higher temperatures than plastics, and therefore do not require expensive equipment to monitor and control the cover sheet to box bottom bonding process. Natural fibre fabric sacks are suitable for packaging of cement or other materials since the trapped air flows out of the sack after the filling operation. Laminated sacks can be micro perforated if desired. Furthermore, cover sheets are small in area and do not consume much material, hence they can be constructed of plastic to provide additional strength to the box bottom when attached. The natural fibre sack body can be laminated to seal the sack, or the cover sheet can be laminated. The lamination of either or both the sack body and the cover sheet is further advantageous because it facilitates heat bonding between the cover sheet and the box bottom of the sack. Where a sack liner is to be used, lamination is not essential, as the coversheet can be stitched, or otherwise similarly affixed, to the sack body.

The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto. 

1. A box bottomed sack comprising: a sack body having one end folded into a box bottom configuration, the sack body constructed from a fabric made from materials selected from a list including materials woven from monoaxially oriented tapes, cotton, jute, hemp, nylon, and polyester; and a cover sheet, attached to the folded end of the sack body, the cover sheet constructed from a fabric made from materials selected from a list including materials woven from monoaxially oriented tapes, cotton, jute, hemp, nylon, polyester and non woven materials including paper, film or foil, the material selected so that exactly one of the sack body and cover sheet are constructed from monoaxially oriented woven tape fabric.
 2. The box bottomed sack of claim 1, further including a liner, attached to the sack body.
 3. The box bottomed sack of claim 2, wherein the liner is open at both ends and is affixed to the ends of the sack body.
 4. The box bottomed sack of claim 2, wherein the liner has both an open end and a closed end, is larger than the sack body in at least 1 dimension, and is affixed to the sack body by its open end.
 5. The box bottomed sack of claim 2, wherein the liner is attached to the sack body by stitching.
 6. The box bottomed sack of claim 2, wherein the liner is micro perforated.
 7. The box bottomed sack of claim 2, wherein the folded end of the sack body includes a self closing valve open to the interior of the liner.
 8. The box bottomed sack of claim 2, wherein the liner has a thickness of about 5-100 μm.
 9. The box bottomed sack of claim 1, wherein the cover sheet is attached to the sack body by an attachment method selected from a list including heat sealing, gluing, sewing, tacking, taping and slit die extrusion.
 10. The box bottomed sack of claim 1, wherein at least one of the sack body and the cover sheet are laminated.
 11. The box bottomed sack of claim 10, wherein the at least one of the sack body and the coversheet are laminated with a material selected from a list including polyethylene, polypropylene, polyolefins, and ethylene vinyl acetate.
 12. The box bottomed sack of claim 10, wherein the cover sheet is attached to the sack body by fusing the sack body and the cover sheet by an method selected from a list including heat sealing, ultrasonic plastic welding, heating plate pressing, heat plate pinning, friction welding and slit die extrusion.
 13. The box bottomed sack of claim 1, wherein the folded end of the sack body includes a valve.
 14. The box bottomed sack of claim 13, wherein the valve is self closing.
 15. The box bottomed sack of claim 13, wherein the valve is disposed between the folded end and the coversheet.
 16. The box bottomed sack of claim 1 including a layer of molten plastic material interposed between the folded end and the cover sheet.
 17. The box bottomed sack of claim 1, wherein the tapes in the monoaxially oriented woven tape fabric have a thickness of about 10-80 μm.
 18. The box bottomed sack of claim 1, the sack body has both ends folded into a box bottom configuration, and the sack includes a second cover sheet, attached to the second folded end of the sack body, the second cover sheet constructed from a material selected from a list including materials woven from monoaxially oriented tapes, cotton, jute, hemp, nylon, polyester and non woven materials including paper, film or foil. 